This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In the mammalian vestibular labyrinth, hair cells are capable of generating axial deformations in response to variations in transmembrane potential. Our understanding of electromechanical transduction in the hair cells depends on precise knowledge of intracellular structure, and efforts to model hair cell physiology are likewise limited to the fidelity of known intracellular geometry. This study focuses on the ultrastructure of vestibular hair cells. More precisely, we are looking at the subcuticular region (below the cuticular plate), trying to visualize and analyze rootlet architecture at the junction of the stereocilia bundle and apical region of the cell. Our main concern is the striated organelle (STO), a unique structure located at the apical end of hair cells (auditory and vestibular sensory cells), just below the cuticular plate. It is particularly prominent in mammalian type I vestibular hair cells. The central hypothesis of this proposal is that striated organelles provide structural and functional connections between the apical and basal parts of the hair cell. The goals of this proposal are to describe the three-dimensional structure of this particular organelle - Aim 1 - and to identify its components (or at least, some of the components) - Aim 2.